The present invention relates to measurement devices which are to be mounted within the oral cavity. Such measurement devices may be sensitive to the concentration of one or more ionic species or to non-chemical parameters such as pressure, temperature, and flow. In accordance with certain preferred embodiments, sensors are provided for telemetric monitoring of intraoral parametric changes at multiple intraoral sites.
Numerous types and configurations of ion sensitive electrodes are known to those skilled in the art. See, for example, the above-referenced U.S. patent application for "Amorphous Metal Oxide Electrodes", Ser. No. 441,902. As discussed in that application, prior art electrodes include discrete elements such as glass electrodes and metal oxide electrodes. As disclosed in application Ser. No. 441,902, an especially useful electrode is one made of an amorphous oxide of a metal selected from the platinum or rhenium groups of metals. Preferably such electrodes are formed by applying such amorphous oxide as the gate material in a field effect transistor. The resulting ion sensitive field effect transistor (ISFET) is highly effective for the detection and measurement of ionic species, especially pH.
One area of considerable research interest involving pH measurements is the measurement of intraoral pH and especially plaque pH. It has long been known that the acidic fermentation products produced by plaque microorganisms in the presence of sugar and carbohydrates are strongly associated with dental caries. See, for example, Stephan, R.M., "Changes in hydrogen-ion concentration on tooth surfaces and in carious lesions", J. Amer. Dental Assn., vol. 27, pages 718-723 (1940); Straffors, A., "Investigations into the bacterial chemistry of dental plaque", Odont. Tidsler. vol. 58, pages 155-341 (1950). Because of this known importance of plaque pH, measurement of plaque pH is now widely accepted as a method of evaluating the effect of carbohydrates on oral health. Yankell, S. L., et al., "In vitro Testing of a New System for Monitoring pH at Multiple Sites", Caries Res., vol. 17, pages 439-443 (1983) which is incorporated herein by reference.
There are, however, considerable difficulties in the measurement of plaque pH and other intraoral parameters of interest using prior art devices. Prior art devices were frequently too large, difficult or objectionable to mount within the patient's mouth and limited in their capacity to monitor events of interest. Yankell, S. L., et al., "Development of Telemetric Intraoral Chemical Sensing Systems", Annual Conference on Engineering in Medicine and Biology (1982). For example, most successful in vivo pH sensing systems to date place the microelectrodes in prosthetic teeth, providing a surface for plaque deposition at an interproximal site adjacent to a natural tooth (Schactele and Jensen, 1982; Firestone, 1982). The same site can be noninvasively observed over time and during various oral functions such as rinsing and chewing. There are, however, several shortcomings in these approaches. Constraints are imposed on subject selection due to the requirements for teeth that are missing or in need of being crowned. With these current systems using glass electrodes, the response time is relatively slow; the high electrode impedance leads to noise problems and the large size of even the smallest glass microelectrode precludes efficient monitoring of multiple sites and makes nonintrusive monitoring at interproximal sites impossible. While the above-referenced paper by Yankell describes a proposed system that avoids many of these problems, it has been found that while it works satisfactorily in vitro it does not perform satisfactorily in vivo.